Yes, NEX is a "live system" with improved bodies and lenses/accessories coming out for it at a good clip. In that sense, buying lenses will not at all be a waste, assuming you can use them. But I agree with nrcole, I would sacrifice on other things and get the NEX-6 (or 7) if you really want the EVF, I would NOT buy that accessory for the F3.

If you can't sell the F3, then go dual-body when you can, you can get tons of flexibility that way.